The present invention relates to an apparatus for observing the suction (aspiration) of a sample (liquid specimen) in an automatic analyzer such as a blood analyzer, and more particularly to an apparatus for observing the suction of a sample having an automatic regulation function for maintaining a favorable detection sensitivity.
Hitherto apparatuses have been known for observing whether a sample, such as a blood sample, is aspirated correctly or not. FIG. 1 shows an example thereof, which is intended to observe the suction of a sample by the change of transmitting light from a photo element.
Numeral 14 denotes a tube for sucking (aspirating) a sample, which is made of a synthetic resin of high transparency. A luminous element 10 such as an LED and a photo sensor 12 such as a photo transistor are disposed opposingly across the sample suction tube 14. A constant current circuit 16 composed of a transistor 18 and a resistance R3 is connected to the luminous element 10. A variable resistor VR is connected to the base B of the transistor 18, and the value of the current flowing in the luminous element 10 is varied by adjusting the variable resistor VR.
On the other hand, resistors R2, R1 are connected to the collector C and emitter E of the photo sensor 12, and the current corresponding to the quantity of light received that has been detected is converted into a voltage and taken out. The resistance R2 is not necessarily required. To the output of the photo sensor 12 is connected a judging circuit 20 for judging whether the sample suction is normal or abnormal depending on the change of the quantity of light transmitted at the time of suction of the sample.
Initially, the sample suction tube 14 is filled up entirely with a cleaning solution, and an air layer is provided at the front end of the tube. The portion of the sample suction tube 14 where the luminous element 10 and photo sensor 12 are disposed is high in transparency, the light transmits well, and the voltage Vp at test point Vp is high. By suction of the sample, when the blood reaches the observing area, the light is shielded by the blood corpuscle components, and the detected voltage Vp becomes low. By a comparator (not shown) in the judging circuit 20, the detected voltage Vp is set in a binary value showing whether the blood is sucked (aspirated) or not. On the basis of the binary signal, it is further judged whether the suction is normal or not. When the sample suction is over, the cleaning solution is poured into the tube, and the residue of the blood sample is washed away.
In this apparatus, incidentally, various fluctuations (scatter) occur. For example, fluctuations of the circuit components, such as the luminous element and the photo sensor, and fluctuations of the tube diameter and transparency are known. In order to maintain a high detection capability by absorbing such fluctuations, it is designed to adjust the current of the luminous element 10 by the variable resistor VR. In this adjustment, it is designed so that the detection voltage Vp at the test point TP may be a specified value in the specific conditions of the state in the sample suction tube 14 (for example, with the tube filled up with a clear liquid).
The existing apparatus had the following problems.
(1) Every time the tube is exchanged, the current of the luminous element must be adjusted by the VR depending on the tube diameter and transparency, and the operation is complicated. PA1 (2) The characteristics of the circuit components vary with the passing of time and change of temperature, and the detection sensitivity is lowered. PA1 (3) The detection sensitivity is also lowered by the contamination of tube or occurrence of injury. PA1 (4) In the case of a thin tube, a slight deviation of position of the tube, or dislocation of the luminous element or the photo sensor may lead to lowering of the detection sensitivity.